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Research Papers

Proof-of-Concept of the Shape Memory Alloy ReseTtable Dual Chamber Lift Device for Pedestrian Protection With Tailorable Performance

[+] Author and Article Information
Jonathan Luntz

e-mail: jluntz@umich.edu

Diann Brei

Mechanical Engineering,
University of Michigan,
2250 G. G. Brown,
Ann Arbor, MI 48109

Nancy L. Johnson

General Motors R&D Vehicle
Development Research Lab,
MC 480-106-256 30500 Mound Road,
Warren, MI 48090-9055

Contributed by Design Innovation and Devices of ASME for publication in the Journal of Mechanical Design. Manuscript received August 4, 2011; final manuscript received December 17, 2012; published online April 22, 2013. Assoc. Editor: Mary Frecker.

J. Mech. Des 135(6), 061008 (Apr 22, 2013) (12 pages) Paper No: MD-11-1333; doi: 10.1115/1.4023552 History: Received August 04, 2011; Revised December 17, 2012

As automobile use expands in population-dense cities across the world, there is a growing need for new approaches to mitigate the consequences to pedestrians of pedestrian/automotive collisions. This is especially challenging for passive approaches since there is an increasing internal space demand that reduces the crush zone between the relatively compliant hood and rigid underhood components. One unique approach is an active hood lift which raises the hood upon detection of a collision with a pedestrian to increase the crush zone. This approach is technically challenging due to the fast and accurate timing which is sensitive to extrinsic factors (including pedestrian height and weight and the need for reusable/automatically resettable functionality. This paper presents a novel hood lift concept: the shape memory alloy ReseTtable (SMArt) dual chamber lift device which is reusable, automatically resettable, and has tunable performance both off-line, and on-line to adjust to extrinsic factors. This device is situated under the rear corners of the hood and stores energy in the form of compressed air in opposing sides of a dual chamber pneumatic cylinder and a high-speed shape memory alloy exhaust valve (SEV) vents the upper chamber within milliseconds to allow the lower chamber to deploy the hood. A general multistage sequential design process is outlined that enables lift timing performance to be tailored by parametric design off-line and by varying operating parameters on-line. A proof-of-concept prototype was built and experimentally characterized for a midsize sedan case study confirming the timing, load capability and stroke of the device on the benchtop and the complete operational cycle in a full-scale automobile hood bay. The impact of additional mass on the lift timing was measured and two on-line adjustable operating parameters (pressure and valve timing) were investigated for their ability to compensate for the mass and other extrinsic effects. While this was a limited study of this new active technological approach to pedestrian safety, it does indicate promise to meet the strict demands of an active lift and a tailorable, resettable/reusable device.

Copyright © 2013 by ASME
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Figures

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Fig. 1

Hood lift concept. Lifting the rear of the hood creates an additional crush distance for pedestrian protection.

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Fig. 2

SMArt dual chamber lift device architecture. Figure shows major functional components.

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Fig. 3

SMArt dual chamber lift device operational cycles. The device, initially with no stored energy, is reset by pumping air into both chambers, storing energy in the device. The SMA exhaust valve system opens, quickly venting the upper chamber, lifting the hood. The hood is lowered by venting the lower chamber after which it can be either reset or completely vented, dissipating energy to the initial state for safe servicing.

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Fig. 4

Architecture of the SEV system

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Fig. 5

SMA secondary valve. SMA wires packaged down the center of an adjustable reset spring pull open a valve plate against the spring.

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Fig. 6

Operation stages of the SMA exhaust valve system

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Fig. 7

Experimental setup for QEV testing

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Fig. 8

Benchtop prototype setup. The primary components of the device are shown.

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Fig. 9

Dual chamber secondary SMA valve prototype

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Fig. 10

Secondary SMA valve opening profile

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Fig. 11

Dual chamber prototype performance at 170 psia

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Fig. 12

Experimental vehicle hood bay testbed. Two devices, mounted at the rear corners of the hood are shown along with the control and measurement equipment.

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Fig. 13

Hood hinge and device. The system and its mountings are shown with the hood removed.

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Fig. 14

Full-cycle hood position and cylinder pressure. The hood height and lower chamber pressure are shown as the device is lifted, lowered, and reset (store energy).

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Fig. 15

Hood position versus time. The hood position reaches the target lift height of 120 mm in 29 ms. The valve and motion timing is indicated on the graph.

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Fig. 16

Additional mass experimental setup. A weight is clamped directly above the lift device.

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Fig. 17

Hood Lift time versus additional mass. Adding mass to the hood has an effect on lift time.

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Fig. 18

Lift time versus cylinder pressure. The lift time can be changed by varying lower chamber pressure. The performance deviates from the model when pressure is too low to quickly actuate the QEV.

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Fig. 19

Lift time versus applied voltage. Lower voltages, and equivalently shorter current bursts provide authority for adjusting lift time.

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